The ability to manipulate the polarization states of radiation has a breadth of applications across the electromagnetic spectrum. For example, in communication systems, polarization multiplexing/diversity can significantly improve data reliability and transmission rate, in which there has been proposed a scheme to reach 100 Gb/s per channel over existing infrastructure; in spectroscopy and sensing applications, variable polarization of the light source is an attractive feature for investigating materials with local symmetry, e.g., molecular chirality; in optical holography, circularly polarized beams make it possible to realize wide-angle holograms with 80% power efficiency over a broad wavelength range, upon illuminating metallic nanorod arrays; and, continuously tunable linear-elliptical polarization significantly simplifies the design of ellipsometry systems, by eliminating the use of Soleil-Babinet compensators or rotating analyzers.
Manipulation of the polarization state of light usually relies on external, bulky, optical components, such as wave plates and polarizers. However, these do not lead to system miniaturization and fast operation, and many such components are lossy over specific wavelength ranges (e.g., known terahertz (THz) frequency continuous polarization converters have a transmission <30%). Previously, it has been demonstrated that the polarization state of spin-polarized lasers and light-emitting diodes can be tuned by varying the amplitude or direction of an applied external magnetic field, achieving a degree-of-circular-polarization (DOCP) of up to 50%. Furthermore, a degree-of-circular-polarization (DOCP) of 98% was achieved in quantum cascade lasers (QCLs) with built-in antennas for selected far-field regions of the emission, albeit pre-determined by the device fabrication process.
Further, for known devices, the polarization property is fixed after fabrication.
Therefore, there is a need to develop low loss devices with controllable polarization.